Process and system for precision glass sheet bending

ABSTRACT

An apparatus and method for precision bending a glass sheet that includes an oven for heating the glass sheet to a temperature near the softening temperature of the glass sheet. A stage for supporting the glass sheet. A pair of reference surfaces on the stage for precisely locating the glass sheet on the stage. At least one bending mechanism on a pair of arms inside the oven for bending an edge portion of the glass sheet. Inward facing first stop surfaces on the arms that contact reference surfaces on the stage for precisely locating the bending mechanism on the arms relative to the stage and the glass sheet.

BACKGROUND

The field of the invention is a device for supporting and accuratelypositioning a large area glass sheet for high precision bending of theglass sheet, and more particularly for localized, high temperature, highprecision bending of opposing edge portions of a large area glass sheethaving a relatively high coefficient of thermal expansion (CTE).

Electronic devices often include a protective cover glass that providesimpact and scratch resistance to the front, display or touch controlportion of the device. Electronic devices, such as cell phones (andother portable devices), LCD flat panel televisions and, householdappliances are trending toward edge to edge transparent front coversthat provide a clean, glossy, seamless and/or frameless design.

No admission is made that any reference cited herein constitutes priorart. Applicant expressly reserves the right to challenge the accuracyand pertinency of any cited documents.

SUMMARY

The invention relies on the design and use of a non deformable carriersupporting a large glass sheet in a perfectly known geometricalreference at room temperature and while heating the glass sheet to ahigh glass reforming or bending temperature (processing temperature).The carrier offers a low thermal expansion and an essentially inelasticmechanical support in the 20-750° C. range enabling the carrier toprovide a non-deformable bearing surface. The carrier also includesregistration surfaces at registration points on the carrier forprecisely aligning the glass sheet on the carrier that are known allover the reforming thermal cycle. The carrier also presents interfaceswith edge bending mechanisms for providing precise local registration ofthe bending mechanisms. The carrier may include a metallic frame forengaging with a bending apparatus conveying system and a non-deformableplate or mold for supporting and molding the glass sheet. The mold maybe made of various materials, such as glass ceramic or Silicon Carbide,that have a low thermal expansion and are essentially inelastic in the20° C. to 750° C. range.

One embodiment of the disclosure relates to an apparatus for preciselybending a glass sheet. The apparatus includes an oven for heating theglass sheet to a temperature near or greater than the annealingtemperature of the glass sheet. A stage having a top support surface forsupporting a sheet of glass, a first edge, an opposing second edge, anda pair of outward facing first reference surfaces on the first edge ofthe stage adjacent to ends of the first edge of the stage. A pair offirst arms having inner ends extending into the oven from a first sideof the oven, a first bending mechanism mounted on the inner ends of thefirst pair of arms inside the oven for bending a first edge portion of aglass sheet on the stage down over the first edge of the stage, and aninward facing first stop surface provided near the inner end of each ofthe first arms in opposition to the pair of first reference surfaces. Apair of second arms having inner ends extending into the oven from asecond side of the oven, and an inward facing second stop surfaceprovided near the inner end of each of the second arms in opposition tothe second edge of the stage. A first moving mechanism for moving thepair of first arms inward toward and outward away from the first edge ofthe stage. Whereby when the stage is located in the oven with a glasssheet to be bent supported on the support surface of stage with a firstedge portion of the glass sheet to be bent extending beyond the firstedge of the stage, the first arms are moved inward toward the stage andthe second arms are moved inward toward the stage until the first stopsurfaces contact the first reference surfaces and the second stopsurfaces contact the second edge of the stage, whereby the stage is heldbetween the first stop surfaces and the second stop surfaces with thefirst edge of stage and the first edge of the glass sheet is preciselylocated relative to and aligned with the first bending mechanism.

Other embodiments of the disclosure relate to such an apparatus asfurther including a lift arm on the inner ends of each of the first armsand the second arms that extend inward from the first and second stopsurfaces. Whereby when the first arms are moved inward toward the stageand the second arms are moved inward toward the stage, the lift armsengage an under-side of the stage and lift the stage such that the stageis resting on the lift arms and the stage is free to translate androtate on the lift arms, whereby as the first stop surfaces contact thefirst reference surfaces and the second stop surfaces contact the secondedge of the stage translates and rotates on the lift arms until all ofthe first stop surfaces are contacting the first reference surfaces andall of the second stop surfaces are contacting the second edge of thestage, whereby the first edge of the stage and the first edge of theglass sheet are precisely located relative to and aligned with the firstbending mechanism.

Other embodiments of the disclosure relate to such an apparatus furtherincluding pair of outward facing second reference surfaces on the secondedge of the stage adjacent to ends of the second edge of the stage andsecond bending mechanism mounted on the inner ends of the second pair ofarms inside the oven. Whereby when the stage is located in the oven witha glass sheet to be bent supported on the support surface of stage witha first edge portion of the glass sheet to be bent extending beyond afirst edge of the stage and a second edge portion of the glass sheet tobe bent extending beyond the second edge of the stage, the first armsare moved inward toward the stage and the second arms are moved inwardtoward the stage until the first stop surfaces contact the firstreference surfaces and the second stop surfaces contact the secondreference surfaces, whereby the stage is held between the first stopsurfaces and the second stop surfaces with the first edge of stage andthe first edge of the glass sheet precisely located relative to andaligned with the first bending mechanism and the second edge of stageand the second edge of the glass sheet precisely located relative to andaligned with the second bending mechanism.

Other embodiments of the disclosure relate to such an apparatus whereinat least one of the pair of first arms and the pair of second arms arespring loaded and the first arms and second arms are moved inward untilthe spring load arms are compressed and apply pressure on the edge ofthe stage.

Other embodiments of the disclosure relate to such an apparatus whereinthe stage further comprises a third edge extending between the firstedge of the stage and the second edge of the stage, a first registrationelement extending upward form the support surface of the stage adjacentto the third edge of the stage, and a second registration elementextending upward from the support surface of the stage adjacent to thethird edge of the stage. The first registration element and the secondregistration element being located on the stage to define a referenceline oriented at a desired orientation with respect to the first edge ofthe stage. Whereby when a glass sheet having a first edge portion to bebent is located on the support surface with a reference edge of theglass sheet extending from the first edge in contact with both the firstregistration element and the second registration element, the first edgeportion of the glass sheet is aligned with the first edge of the stage.

Other embodiments of the disclosure relate to such an apparatus whereinthe stage further comprises a clamp mounted adjacent to the third edgeof the stage, the clamp having a clamp surface for clamping a glasssheet in place on the support surface. Whereby when the glass sheet islocated on the support surface with the reference edge of the glasssheet in contact with both the first registration element and the secondregistration element and a reference point on the glass sheet is alignedwith and clamped in place on the stage by the clamp surface, the glasssheet is precisely located and secured in place on the stage with thefirst edge portion of the glass sheet aligned with and extending a firstdesired distance beyond the first edge of the stage.

Other embodiments of the disclosure relate to such an apparatus whereinthe clamp surface is formed of two or more separate contact surfaces.

Other embodiments of the disclosure relate to such an apparatus furtherincluding a pair of outward facing second reference surfaces on thesecond edge of the stage adjacent to each end of the second edge of thestage, and a second bending mechanism mounted on the inner ends of thesecond pair of arms inside the oven. Whereby when the glass sheet islocated on the support surface with the reference edge of the glasssheet in contact with both the first registration element and the secondregistration element and a reference point on the glass sheet is alignedwith and clamped in place on the stage by the clamp surface, the glasssheet is precisely located and secured in place on the stage with thefirst edge portion of the glass sheet aligned with and extending a firstdesired distance beyond the first edge of the stage and the second edgeportion of the glass sheet aligned with and extending a second desireddistance beyond the second edge of the stage; and whereby when the firstarms are moved inward toward the stage and the second arms are movedinward toward the stage until the first stop surfaces contact the firstreference surfaces and the second stop surfaces contact the secondreference surfaces, the stage is held between the first stop surfacesand the second stop surfaces with the first edge of stage and the firstedge of the glass sheet is precisely located relative to and alignedwith the first bending mechanism and second edge of stage and the secondedge of the glass sheet is precisely located relative to and alignedwith the second bending mechanism.

Other embodiments of the disclosure relate to such an apparatus whereinthe first bending mechanism and second bending mechanism each include abiasing apparatus for pushing and bend the corresponding first edgeportion of the glass sheet and the second first edge portion of theglass sheet down over a corresponding one of the first edge of the stageand a second edge of the stage.

Other embodiments of the disclosure relate to such an apparatus whereinthe first bending mechanism and second bending mechanism each include alocal heating apparatus for heating the corresponding first edge portionof the glass sheet and the second edge portion of the glass sheet to atemperature near the softening temperature of the glass sheet, such as atemperature between the annealing temperature and the softeningtemperature of the glass.

Other embodiments of the disclosure relate to such an apparatus whereinthe first bending mechanism and second bending mechanism each include alocal heating apparatus for heating the corresponding first edge portionof the glass sheet and the second edge portion of the glass sheet to atemperature near the softening temperature of the glass sheet, such as atemperature between the annealing temperature and the softeningtemperature of the glass.

Other embodiments of the disclosure relate to such an apparatus furtherincluding a lift arm on the inner ends of each of the first arms and thesecond arms that extend inward from the first and second stop surfaces.Whereby when the first arms are moved inward toward the stage and thesecond arms are moved inward toward the stage, the lift arms engage anunder-side of the stage and lift the stage such that the stage isresting on the lift arms and the stage is free to translate and rotateon the lift arms, whereby as the first stop surfaces contact the firstreference surfaces and the second stop surfaces contact the secondreference surfaces the stage translates and rotates on the lift armsuntil all of the first stop surfaces are contacting the first referencesurfaces and all of the second stop surfaces are contacting the secondreference surfaces, whereby the first edge of the stage and the firstedge of the glass sheet are precisely located relative to and alignedwith the first bending mechanism and the second edge of the stage andthe second edge of the glass sheet are precisely located relative to andaligned with the second bending mechanism.

Other embodiments of the disclosure relate to a method of preciselybending at least one edge portion of a glass sheet including the stepsof: locating a glass sheet on a support surface of a stage having afirst edge and an opposing second edge, with a first edge portion of theglass sheet extending beyond the first edge of the stage, the first edgeof the stage having pair of spaced outward facing first referencesurfaces; providing an elongate first bending mechanism inside the ovenfor bending a first edge portion of a glass sheet on the stage down overthe first edge of the stage, the bending mechanism having a pair ofspaced inward facing first stop surfaces in opposition to the pair offirst reference surfaces; providing a pair of spaced inward facing firststop surfaces in opposition to the second edge of the stage; locatingthe stage with the glass sheet supported thereon in a bending oven andheating the glass sheet to a temperature between the annealingtemperature and the softening temperature of the glass sheet; and movingthe first bending mechanism and moving the second stop surfaces inwardtoward the stage until the first stop surfaces contact the firstreference surfaces and the second stop surfaces contact the second edgeof the stage, whereby the stage is held between the first stop surfacesand the second stop surfaces with the first edge of stage and the firstedge portion of the glass sheet is precisely located relative to andaligned with the first bending mechanism.

Other embodiments of the disclosure relate to such a method furtherincluding the steps of: providing pair of spaced first lift armsextending inward from the first heating device and a pair of spacedsecond lift arms extending inward from the second stop surfaces; andmoving the first bending mechanism and moving the second stop surfacesinward toward the stage until the first stop surfaces contact the firstreference surfaces and the second stop surfaces contact the second edgeof the stage, whereby the lift arms engage an under-side of the stageand lift the stage such that the stage is resting on the lift arms andthe stage is free to translate and rotate on the lift arms, whereby asthe first stop surfaces contact the first reference surfaces and thesecond stop surfaces contact the second edge of the stage translates androtates on the lift arms until all of the first stop surfaces arecontacting the first reference surfaces and all of the second stopsurfaces are contacting the second edge of the stage, whereby the firstedge of the stage and the first edge of the glass sheet are preciselylocated relative to and aligned with the first bending mechanism.

Other embodiments of the disclosure relate to such a method furtherincluding the steps of: locating a glass sheet on a support surface of astage having a first edge and an opposing second edge, with a first edgeportion of the glass sheet extending beyond the first edge of the stageand a second edge portion of the glass sheet extending beyond the secondedge of the stage, the first edge of the stage having pair of spacedoutward facing first reference surfaces and the second edge of the stagehaving pair of spaced outward facing second reference surfaces;providing an elongate second bending mechanism inside the oven forbending a second edge portion of a glass sheet on the stage down overthe second edge of the stage, the second stop surfaces being located onthe second bending mechanism; and moving the first bending mechanism andsecond bending mechanism inward toward the stage until the first stopsurfaces contact the first reference surfaces and the second stopsurfaces contact the second reference surfaces, whereby the stage isheld between the first stop surfaces and the second stop surfaces withthe first edge of stage and the first edge portion of the glass sheetprecisely located relative to and aligned with the first bendingmechanism, and the second edge of stage and the second edge portion ofthe glass sheet precisely located relative to and aligned with thesecond bending mechanism.

Other embodiments of the disclosure relate to such a method wherein thestage further comprises a third edge extending between the first edge ofthe stage and the second edge of the stage. Providing a firstregistration point and a second registration point on the stage adjacentto the third edge of the stage, such that registration point and asecond registration point define a reference line oriented at a desiredorientation with respect to the first edge of the stage whereby.Locating the glass sheet on the stage with a reference edge of the glasssheet aligned with both the registration point and the secondregistration point, whereby the first edge portion of the glass sheet isaligned with the first edge of the stage.

Other embodiments of the disclosure relate to such a method furtherincluding the steps of: providing a third registration point on thestage; locating the glass sheet on the stage with a reference edge ofthe glass sheet aligned with both the first registration point and thesecond registration point, and the reference point of the glass alignedwith the third registration point on the glass, whereby, the glass sheetis precisely located and secured in place on the stage with the firstedge portion of the glass sheet aligned with and extending a firstdesired distance beyond the first edge of the stage and the second edgeportion of the glass sheet aligned with and extending a second desireddistance beyond the second edge of the stage; and clamping the glassagainst the stage at the third reference point.

Other embodiments of the disclosure relate to such a method wherein thefirst bending mechanism and second bending mechanism each include abiasing apparatus for pushing and bending the corresponding first edgeportion of the glass sheet and the second edge portion of the glasssheet down over a corresponding one of the first edge of the stage and asecond edge of the stage.

Other embodiments of the disclosure relate to such a method the firstbending mechanism and second bending mechanism each include a localheating apparatus for heating the corresponding first edge portion ofthe glass sheet and the second edge portion of the glass sheet to atemperature near the softening temperature of the glass sheet, such as atemperature between the annealing temperature and the softeningtemperature of the glass.

Other embodiments of the disclosure relate to such a method wherein thefirst bending mechanism and second bending mechanism each include alocal heating apparatus for heating the corresponding first edge portionof the glass sheet and the second edge portion of the glass sheet to atemperature near the softening temperature of the glass sheet, such as atemperature between the annealing temperature and the softeningtemperature of the glass.

Other embodiments of the disclosure relate to such a method furtherincluding the steps of: providing pair of spaced first lift armsextending inward from the first heating device and a pair of spacedsecond lift arms extending inward from the second heating device; andmoving the first bending mechanism and moving the second bendingmechanism inward toward the stage until the first stop surfaces contactthe first reference surfaces and the second stop surfaces contact thesecond edge of the stage, whereby the lift arms engage an under-side ofthe stage and lift the stage such that the stage is resting on the liftarms and the stage is free to translate and rotate on the lift arms,whereby as the first stop surfaces contact the first reference surfacesand the second stop surfaces contact the second edge of the stagetranslates and rotates on the lift arms until all of the first stopsurfaces are contacting the first reference surfaces and all of thesecond stop surfaces are contacting the second edge of the stage,whereby the first edge of the stage and the first edge of the glasssheet are precisely located relative to and aligned with the firstbending mechanism and the second edge of the stage and the second edgeof the glass sheet are precisely located relative to and aligned withthe second bending mechanism.\

Other embodiments include a method or system for bending a glass sheetin which the glass sheet being bent meets the following criteria:CTE×D×ΔT≧2×ST, where CTE is the coefficient of thermal expansion of theglass sheet, D is the largest dimension of the glass sheet, ΔT is thechange in temperature of the glass sheet during bending of the glasssheet, and ST is the specified tolerance for the bent glass sheet.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic edge view of a bent sheet of glass (not drawn toscale) according to an embodiment hereof;

FIG. 2 is a schematic side view of a conveyor and bending oven accordingto an embodiment hereof;

FIG. 3 is a perspective top view of a registration carrier according toan embodiment hereof;

FIG. 4 is an explanatory schematic plan view of the registration carrierof FIG. 3;

FIG. 5 is an explanatory schematic side view of the registration carrierin the bending zone of the bending oven;

FIG. 6 is an explanatory schematic plan view of the registration carrierin the bending zone of the bending oven;

FIG. 7 is a perspective bottom view of the registration carrier of FIG.3;

FIG. 8 is a partially exploded perspective view of a conveyor caraccording to one embodiment hereof and the registration carrier of FIG.3

FIGS. 9 through 11 are partial side views of the registration carrier ina bending oven illustrating operation of an embodiment of a heating andbending device positioning mechanism;

FIG. 12 is a schematic illustration of the effects of thermal expansionon a system as shown in FIG. 7 through 11; and

FIG. 13 is a schematic illustration of the effects of thermal expansionon a system not constructed as shown in FIGS. 7 through 11.

DETAILED DESCRIPTION

FIG. 1 is schematic illustration (not drawn to scale) of an embodimentof a formed or shaped glass article 1 that may be used as a glass coveror fascia for an electronic device or architectural component. Such aglass cover (or cover glass) 1 may be shaped, such as by molding,bending or sagging, such that it has rearward extending side portions 3and 5 a generally planar central front panel portion 7 and. The central,side and inner portions of the glass fascia may be substantiallyflat/planar in configuration, or may be slightly curved/bowed orotherwise shaped.

Glass covers for devices with electronic displays or touch controls areincreasingly being formed of thin glass that has been chemicallystrengthened using an ion exchange process, such as Gorilla® glass fromCorning Incorporated, in order to provide a thin, lightweight glasscover with enhanced fracture and scratch resistance, as well as enhancedoptical and touch performance for these devices. Ion exchangeableglasses typically have a relatively higher CTE than non-ion exchangeableprocess. Ion exchangeable glasses may, for example, have a high CTE inthe order of 70×10⁻⁷ C⁻¹ to 90×10⁻⁷ C⁻¹. The thin glass sheets may havea thickness of up to about 1.5 mm, up to about 1 mm, up to about 0.7 mm,or in a range of from about 0.5 mm to about 1.5 mm, or from about 0.5 mmto about 0.7.

Assembly tolerances in the order of +/−0.5 mm or less are often requiredto provide the desired quality look, feel, fit and finish for anelectronic or other device. Such tolerances are difficult to achievewhen performing high temperature, localized, high precision bending ofrelatively high CTE or relatively large glass sheets, e.g. a sheetshaving a dimension of over 1 m, of ion exchangeable glass. When heatinga relatively large glass sheet or a relatively high CTE glass sheet to atemperature that softens the glass to the point that it can be bent orformed to the desired shape, the sheet of glass may expand by as much as10 mm in one or more directions. This expansion of the glass createschallenges in maintaining high precision tolerances when heating andbending the glass sheet. The relationship between the size, CTE and highprecision tolerances for a bent/formed glass may be expressed be bymultiplying the CTE of the glass sheet, the largest dimension D of theglass sheet and the change in temperature ΔT during bending/forming ofthe glass sheet (CTE×D×ΔT). When CTE×D×ΔT is larger than 2 or more, or 4or more times the specified tolerance ST for the bent/formed glass sheet(CTE×D×ΔT≧2×ST), then precision forming such a glass sheet without adevice or process as described herein will be a challenge. After bendingthe ion exchangeable glass to the correct shape, the glass is ionexchanged to provide the desired chemical strengthening or tempering ofthe glass sheet.

The present invention provides a solution for precision shaping of largeglass sheets, particularly relatively large sheets of relatively highCTE glass, using a localized high temperature bending processes, andmore particularly relatively thin, relatively, relatively high CTEsheets. However, it will be appreciated that a precision carrier andpositioning device as described herein may be employed in single zoneheating glass bending processes that heats the entire glass sheet to asubstantially uniform temperature for bending, as well as in localizedheating glass bending process that heat just the portions of the glasssheet being bent to a temperature near the softening temperature of theglass, such as a temperature between the annealing temperature and thesoftening temperature of the glass.

Terms such as “rearward” or “downward” are used for convenience ofdescription in this description and the appended claims and should notbe interpreted as requiring a certain orientation of the glass sheet,other elements, or direction of bending of the glass.

The term “relatively large” or “large” as used in this description andthe appended claims in relation to a glass sheet means a glass sheethaving a dimension of 1 meter or more on at least one direction.

The term “relatively high CTE” or “high CTE” as used in this descriptionand the appended claims in relation to a glass or a glass sheet means aglass or glass sheet having a CTE of at least 70×10⁻⁷ C⁻¹.

The term “relatively thin” or “thin” as used in this description and theappended claims in relation to a glass sheet means a glass sheet havinga thickness of up to about 1 mm, up to about 0.7 mm, or in a range offrom about 0.5 mm to about 1 mm, or from about 0.5 mm to about 0.7 mm.

In order to locally bend or form a flat glass sheet into a desiredshape, the glass sheet is typically supported on a frame or mold. Theglass sheet and the mold are then placed in a bending furnace and thefurnace is heated to a temperature between the annealing temperature andthe softening temperature of the glass. The glass sheet may then beallowed to sag, e.g. deform to the shape of the mold under its ownweight, or a force may be applied to the glass sheet to aid in thedeformation of the glass sheet. The glass sheet is then cooled andremoved from the furnace, and the glass sheet is removed from the mold.

As schematically illustrated in FIG. 2, in order to form a plurality ofglass sheets 1 in a continuous fashion, a plurality of molds 10 may belocated on continuously moving conveyor 11 for conveying a plurality ofglass sheets 1 placed on the molds through an elongate bending furnace21 in a serial fashion. Glass sheets are loaded onto the molds at roomtemperature upstream from the furnace. The furnace may have a pluralityof zones of different temperatures. The first of these zones is apreheating zone 23, in which the glass sheets are heated to atemperature close to the annealing temperature of the glass. Thepreheating zone may be comprised of a plurality of pre-heating zones 23a, 23 b, etc. of increasing temperature for slowly heating the glasssheets. The next zone is a bending zone 25, where the glass sheets arebrought to a processing or bending temperature, such as a temperaturebetween the annealing temperature and the softening temperature of theglass, for example, a temperature of about 600° C. The bending zone 25is long enough to provide the glass sheets sufficient time to graduallybend by gravity until it assumes the shape of the frame. Alternatively,a force may be applied to the edge portions of the glass sheets to morerapidly bend the glass sheets 1. The glass sheets are then cooled in acooling zone 27 to room temperature and exit the output end of thetunnel furnace. The glass sheets may alternatively be cooled in the air,eliminating the need for the cooling zone in the bending oven. Theformed and cooled glass sheets 1 are then removed from the molds 10downstream from the oven.

In order to precisely form the bent portions 3 and 5 of a glass sheet 1to high tolerances, the glass sheet 1 must be precisely positioned onthe molds 10 and must remain precisely positioned throughout thepre-heating and bending process. As previously described, when heating arelatively large or a relatively high CTE sheet of glass to the bendingor processing temperature, for example, a temperature of a at least 600°C., the sheet may expand by as much as 10 mm in one or more directions.As the glass sheet expands during heating, the sheet is likely to shiftone way or the other on the mold 10. As a result of this shifting, theglass sheet 1 may no longer be precisely positioned on the mold 10 andwill not be precisely shaped to the desired shape, such a, for example,a precisely, symmetrically bent sheet of glass 1 as illustrated in FIG.1.

FIG. 3 illustrates a flat, planar glass sheet 1 on a registrationcarrier 100 according to an embodiment hereof for symmetrically bendingopposing side edge portions 3 and 5 of the glass sheet 1, while acentral portion 7 of the glass sheet remains flat. The registrationcarrier 100 is designed for accurately registering/locating the glasssheet 1 on the carrier and retaining the glass sheet in this position onthe carrier 100 throughout the glass bending process. The registrationcarrier may include a mold or stage 107 mounted on a base or frame 108made of steel having stable thermal and mechanical properties atbending/processing temperatures, for example refractory steel type ASI310. The glass sheet 1 is precisely placed (registered) on the stage107, with the side edge portions 3 and 5 of the glass sheet extending anequal distance beyond opposing edges 103 and 105 of a rigid stage 107.

The stage has a precisely formed or machined rigid, substantiallynon-deformable, inelastic, flat/planar top support surface forsupporting the flat, planar central portion 7 of the glass sheetthroughout the glass heating and bending process. However, it will beappreciated that the stage may alternatively be curved or bowed toimpart a curve or bow in the central portion of the glass sheet or theside portions of the glass sheet. As such, the term “substantiallyplanar” as used herein and in the appended claims is intended to meanplanar, as well as slightly curved or bowed, for example a convex orconcave curvature in one or more directions having a radius of up to 100cm. The edges 103 and 105 of the stage may be precisely machined tomatch the desired curvature or bend of the edge portions 3 and 4 of theglass sheet. Similarly, the edge regions of the top surface of the stagemay also be contoured or inclined, e.g. with beveled or curving edgeportions, for imparting a desired shape to the edge portions 3 and 5 ofthe glass sheet. The stage may be formed of a rigid material having alow coefficient of thermal expansion (CTE) in order to provide a stable,non-deformable support surface for the glass sheet in a perfectly knowngeometrical reference throughout the process. For example, the stage maybe formed of a material having a CTE of no more that 10×10⁻⁶ K⁻¹, or nmore than 6×10⁻⁶ K⁻¹ The stage may also be made of various materialshaving a low thermal expansion that are essentially elastic in the 20°C. to 750° C. range, in order to avoid permanent deformations fromdeveloping in the stage. Such deformations may occur if materials suchas stainless steel are used, due to the accumulation of thermalgradients upon repeated heating up and cooling of the stage. Forexample, the stage may be formed of a refractory non-metallic material,such as ceramic, glass-ceramic, silicon carbide (SiC) or other rigid,non-deformable. The stage may be formed of an insulating material, inorder to minimize thermal transfer between the glass and the stage. Thestage may also be formed with a thickness of no more the 1 cm in orderto further minimize the thermal inertia of the stage and minimize thethermal impact of the stage on the glass sheet during processing.

The operation of the registration carrier 1 will now be described withreference to FIG. 4, which is an explanatory schematic plan view of theregistration carrier 100 of FIG. 3. Registration of the glass sheet 1 ina precise position on the stage 107 is achieved using three referencepoints A, B, and C on the stage. Reference point A is a fixed referencepoint located precisely midway between the side edges 103 and 105, e.g.at a location that is an equal distance from both side edges 103 and 105of the stage. By fixed, it is meant that once the glass sheet isprecisely registered on the stage 107, a corresponding reference pointAG on the glass sheet, which is precisely located midway between theedges 103 and 105 of the glass sheet, is registered with and fixedrelative to reference point A of the registration carrier and does notmove relative to the stage 107 throughout the glass heating and bendingprocess. Reference points B and C are non-fixed or moving referencepoints, which means that corresponding points BG and CG on the glasssheet 1 move relative to reference points B and C on the registrationcarrier and move relative to the stage 107 as the glass sheet expandsduring the heating and bending process.

Reference points B and C are defined by registration surfaces or element109A and 109B that extend upward from the support surface of the stage.The registration elements 109A and 109B may be formed by registrationrollers or registration posts formed of silicate aluminates, or othersuitable material having suitable mechanical properties and machineability. The registration rollers or posts are mounted on the stage 107in precisely positioned holes formed in the stage adjacent a third edgeof the stage extending between the first and second edges of the stage.The rollers or posts are precisely positioned on the support surface toprecisely define a fixed reference line L perpendicular to the edges 103and 105 of the stage. Reference point A is defined by a contact surface111 of a clamp 113. The clamp 113 is precisely positioned relative andaffixed to the stage 107 or the frame 108, in order to preciselyposition the contact surface 111 at reference point A midway between theedges 103 and 105 of the stage 107. The posts or rollers 109A and 109B,the clamp 113 and the contact surfaces 111 may be formed of refractorysteel (type ASI 310 for example) or other suitable material. It will beappreciated that the stage 107 may be formed of shapes other than theillustrated rectangular shape and the reference line L may be orientatedrelative to the edges of the stage at an angle other than a right angle.Moreover, the reference points A, AG (and the clamp) may not be centeredequidistant from each edge 103, 105 of the stage.

In order to precisely locate a glass sheet 1 on the registration carrier100, the glass sheet 1 is located on the stage 107 of the registrationcarrier by first precisely registering an edge 9 of the glass sheet withthe reference line L on the registration carrier. Next, reference pointAG on the glass is precisely registered with reference point A on theregistration carrier. In order to register the edge 9 of the glass sheetwith the reference line L, first the central portion 7 of the glasssheet 1 is placed flat on the rigid stage 107 of the registrationcarrier 100, with edge portions 3 and 5 of the glass sheet extendingbeyond the edges 103 and 105 of the stage 107. The glass sheet 1 is thenpushed/translated on the stage toward the rollers 109A and 109B, so thatan edge 9 of the glass sheet 1 is pressed against and in contact withthe peripheral surfaces of the rollers 109A and 109B. The edge 9 of theglass sheet 1 is now precisely registered with the reference line Ldefined by the rollers 109A and 109B. Next, the glass sheet istranslated to the left or right on the stage as viewed in FIGS. 3 and 4,while retaining the edge 9 of the glass sheet in contact with therollers 109A and 109B, until reference point AG on the glass sheet isprecisely registered with reference point A on the registration carrier.Retaining the edge 9 of the glass sheet in contact with the rollers (orposts) ensures that the edge of the glass sheet remains in preciseregistration with the reference line L as the glass sheet 1 is moved onthe stage 7. Once point AG on the glass sheet is precisely registeredwith reference point A, then clamp 113 is closed such that the contactsurface 111 of the clamp presses down on a top surface of the glasssheet and securely clamps the glass sheet between the contact surface111 and the stage 107. Reference point AG on the glass sheet is thussecurely fixed by the clamp relative to the reference point A andrelative to the stage 107. The glass sheet is now precisely located andsecured in place on the stage 107 of the registration carrier 100 byrollers 109A and 109B and clamp 113. A biasing force (arrow F) mayoptionally be applied to an opposing edge 8 of the glass sheet 1 inorder to press the edge 9 of the glass sheet against the rollers 9 a and9B and help ensure that the edge 9 of the glass sheet remains in contactwith the rollers in registration with reference line L.

It may be important to avoid marring the surface of the glass sheet withthe contact surface 111 of the clamp 113, in order to maintain theappearance, optical quality and structural integrity/strength of theglass sheet 1. As illustrated in FIG. 3, the clamp may be forked orbifurcated, such that the contact surface is bifurcated into twoseparate, spaced apart contact surfaces 111. Several objectives areachieved by bifurcating the contact surface 111 into two parts. First,bifurcating the contact surface into two spaced apart contact surfacesspreads the contact force applied by the clamp over a larger area on thesurface of the glass sheet, thereby minimizing the surface deformationof the glass sheet caused by the force applied by the clamp. Second,using two spaced apart, relatively small contact surfaces to spread outthe contact force, rather than using a single large contact surface,minimizes the surface area on the glass sheet that is contacted by theclamp.

It is important to minimize the area on the glass sheet that iscontacted by the clamp, so that should the surface of the glass sheet bemarred by contact with the contact surface of the clamp, any suchmarring of the surface of the glass is likewise minimized. Minimizingthe area of contact between the clamp and the glass sheet also minimizesthe thermal impact that the clamp has on the glass sheet, which cancause the glass to ripple or bend due to thermal stresses near thecontact area. The total surface area of the contact surfaces 111 shouldbe large enough relative the total contact force to prevent permanentmarks or deformations on the surface of the glass sheet. Pressureapplied by the clamp may be as low as 10 g/cm2, depending on theviscosity of the glass at processing temperatures, in order to preventmarring of the glass. An example of a suitable surface area for thecontacting surface relative to a contacting force applied by the clampis 20 to 50 cm² in total clamp surface area associated with a 2 to 5 Ncontacting force. The clamping force may be provided by a fixed deadload (e.g. the weight of or a weight on the clamp), by a closing theclamp with a spring having a set spring force, or closing the clamppneumatically, or by some other mechanically means with a pressurecontrol. The contact surface 111 may alternatively be formed of a singlecontact surface or by three or more contact surfaces, rather that theillustrated two contact surfaces 111. The contact surfaces should beclose enough together, for example, no further apart than about 50 mm,in order to approximate a single point, namely reference point A.

When the glass sheet 1 is heated from near room temperature to thebending temperature of the glass sheet, the glass sheet expands by up to10 mm in it's length-wise and width-wise dimensions. The solid lines 8,9, 13 and 15 in FIG. 4 show the original size of the glass sheet whenfirst precisely locate on the registration carrier 100 as previouslydescribed herein. The solid line 9 and dashed lines 8 a, 13 a and 15 ashow the expanded size of the glass sheet 1 after the sheet is heated toits bending temperature in the bending oven. The clamp 113 and therollers 109A and 109B retained the reference point AG on the glass sheetand the edge 9 of the glass sheet in registration with reference point Aand reference line L, respectively, on the stage 107. As a result, asthe glass sheet is heated and expands, the length of the glass sheetincreases equally on both sides of reference point A, AG (e.g. from 13and 15 to 13 a and 15 a) and the glass sheet remains preciselysymmetrically positioned on the stage 107 with the edge portions 3 a and5 a extending beyond the edges of the stage 107 by an equal distance. Itwill be appreciated that the portions 3, 3 a and 5, 5 a of the glasssheet may extend beyond the edges of the stage 107 by differentdistances, such that the glass sheet is not symmetrical after bending,or just a single edge of the glass sheet may bent. In any event, thelocation of the glass sheet on the stage at the bending temperature(represented in dash lines) can be precisely known and reproducible witha registration carrier as described herein.

As previously described herein, the entire glass sheet 1 may be heatedto a bending temperature between the annealing temperature and thesoftening temperature of the glass sheet in the bending zone 25 in asingle heat zone process. Alternatively, the pre-heating zones 23 andthe bending zone 25 may be maintained at temperatures that heat theglass sheets in the bending zone to a temperature that is near but belowthe bending temperature, e.g. below the annealing temperature of theglass. A localized heating device in the bending zone 25 may then heatonly the edge portions 3 and 5 of the glass sheet that are to be bent upto the bending temperature. Alternatively, just portions of the glasssheet over the edges 103, 105 of the stage may be heated to the bendingtemperature, with the outermost edge portions 3, 5 of the glass sheetremaining below the bending temperature of the glass. Keeping theoutermost edge portions 3, 5 of and the central portion 7 the glasssheet below the bending temperature assures that these portions of theglass sheet remain flat/planar and only the portions of the glass sheetthat are to be bent are heated and bent. In any event, the portions 3 aand 5 a of the glass sheets to be bent are heated to the bendingtemperature and bent downward until they conform to the edges 103 and105 of the stage 107, as schematically illustrated in FIG. 2. The edgeportions 3 a and 5 a of the glass sheets may be bent downward under theforce of gravity alone. However, when bending a relatively thin glasssheet, relying on gravity alone to bend the edge portions downward maybe unsatisfactorily slow and unreliable due to the light weight of theglass sheet. It may be advantageous to apply a force to the edgeportions 3 a and 5 a of relatively thin glass sheets in order toincrease the speed and reliability of the bending process in the bendingzone.

When a bending mechanism is employed to apply localized heating and/oran external force to bend the glass sheets, then a locating orregistration mechanism may need to be provided to ensure accuratepositioning of the bending mechanism relative to the edge portions ofthe glass sheet, so that the glass sheets are bent with the desired highprecision tolerances. The bending mechanism may include a localizedheater and/or a force apply device. Localized heaters must be accuratelylocated at the correct position and distance relative to and parallel tothe edge portions 3 a and 5 a of the glass sheet 1, in order to raisethe correct portions of the glass sheet to the bending temperature.Failure to heat the correct portions of the glass sheet to the bendingtemperature could result in failure of the glass sheet to end preciselyand evenly, failure of the glass to bend if just gravity is beingemployed to bend the glass or fracture, or may cause the glass to breakif a force applying device (or bending device) is employed. Likewise,the force applying devices must be accurately positioned at the correctdistance from and parallel to the edge portions 3 a and 5 a of the glasssheet, in order to ensure precise bending of the glass sheet.

FIGS. 5 and 6 schematically illustrate an embodiment of a mechanism 200for precisely locating a localized heating device and/or bending forceapplying device relative to each edge portion 3 a and 5 a of the glasssheets 1 in the bending zone 25 of the bending oven. Four arms 210, 211and 220, 221 extend from outside the bending oven into the bending zoneof the bending oven. The arms 220 and 221 on one side of theregistration carrier 100 may be spring loaded, for example with springs265 and 267, or other pneumatic or hydraulic shock absorbing, biasingdevice. Any suitable moving mechanisms 215, 217, such as, for example,high precision stepper motors, hydraulic cylinders or pneumaticcylinders, are located outside the bending oven for moving the armstoward and way from the registration carrier 100. The moving mechanismsare located outside the bending zone so as to be in a location that isat room temperature, protected from the high bending temperature insidethe bending zone 25. Forming tools, such as local heaters 212 and 222and force applying/force applying devices 214 and 224 may be located oninner ends of the moving arms inside the bending zone 25 of the bendingoven. The heaters 211 may be any suitable local heating device, such asradiant heaters. The force applying devices may be any suitable localforce application devices, such as mechanical pushers or air nozzles.The heaters and force applying devices may be elongate devices that acton the entire length of the edge portions 3 a and 5 a of the glasssheet. The elongate heaters 212, 222 and force applying devices 214, 224are precisely mounted on inner ends of the arms parallel to the edges103 and 105 of the stage. The arms 210 and 211 may be connected togetherfor synchronized movement toward and away from the stage 107. Similarly,arms 220 and 221 may be connected together for synchronized movementtoward and away from the stage 107. The motion of arms 220 and 221 mayalso be synchronized with the motion of arms 210 and 211. With thisconstruction, the heaters and force applying devices are maintainedsubstantially parallel to the edges of the stage as the heaters andforce applying devices are moved toward and away from the stage on thearms.

It will be appreciated that, although FIG. 2 illustrates the edgeportion 3 and 5 of the glass sheet as the leading and trailing edges ofthe glass sheet on the conveyor, it may be advantageous to rotated theregistration carrier 100 by 90 degrees compared to FIG. 2 so that theedges 8 and 9 of the glass sheet are the leading and trailing edges ofthe glass sheet on the conveyor. In this way, the arms 210, 211, 212 and222 and the moving means 215 and 217 may be located to either side ofthe conveyor.

With reference now to FIG. 7, which is a bottom view of the registrationcarrier 100 showing the construction of the frame 108 of theregistration carrier 100 according to one embodiment hereof. The frame108 includes side rails 225 and 226 connected by cross-rails 229. Thelower surfaces of the ends of the side rails are tapered or sloped,forming ramps 227 and 228 on the ends of the side rails. A connectingrod 230 is mounted to the underside of the frame 108. Bearings 231 and237 are mounted on either end of the connecting rod. As shown in FIG. 8,a conveyor car 240 includes a frame with upward opening forks 241, 243mounted to the frame. The conveyor car is mounted on the conveyor 11 andthe registration carrier is supported on the conveyor car for movementwith the conveyor. When the registration carrier 100 is located on theconveyor car, the bearings 231 and 237 on the underside of the frame 108of the registration carrier are releasably received in the forks 241,243 on the conveyor car frame, and the registration carrier frame 108rests on top of the conveyor car frame. The registration carrier is thusmounted on the conveyor car for transport through the bending oven.

With reference now to FIGS. 9 through 11 (in which the heaters 212 andthe force applying devices 214 have been omitted for clarity), the innerends of the arms 210, 211, 220, 221, only one of which is shown in FIGS.9 through 11, each include a lift arm 251 with a lift wheel 251rotationally mounted on the end of the lift arm. A precision stopsurface 255 is formed in or provided on each lift arm 251. A metal cap261 is mounted on each corner of the stage 107 in order to protect thecorners of the rigid stage from impacts. The caps 261 each include aprecision formed reference surface 263 on the side of the cap facing thecorresponding moving arm 210, 211, 220, 221.

As illustrated in sequence on FIGS. 9 through 11, the arms 210, 211 and220, 221 are retracted as the registration carrier carrying the glasssheet moves into the bending zone 25 of the bending oven. The conveyoris stopped when the caps 261 on the registration carrier are alignedwith the arms 210, 211 and 220, 221. The arms 210, 211 and 220, 221 arethen moved in toward the registration carrier. As the arms move inward,the lift rollers 253 on the arms contact the ramps 227, 228 on the siderails 225, 226 of the carrier frame 108 and lift the registrationcarrier frame 108 up off of the conveyor frame 240 as illustrated inFIG. 10. The lift rollers 253 and rails 225, 226 are precisely formed inorder to precisely control the height of the stage 107 relative to theends of the lift arms. The lift rollers contact the lower surfaces ofthe rails 225 and 226, thereby precisely lifting each corner of thecarrier a precise distance relative to the ends of the lift arms. Itwill be appreciated the rollers 253 may optionally be dispensed with andreplaced with an inclined contact or lift surfaces on the ends of thearms.

As the arms 210, 211 and 220, 221 continue to move inward, the stopsurfaces (or just stops) 255 on the arms contact the reference surfaces263 on the caps on the stage as illustrated in FIG. 11. The stop surfacegently pushes the carrier until it contacts the stop surface on theopposing arm. As the stops 255 on opposing arms 210-210 and 211-221 bothcontact the reference surfaces 263 on the corresponding caps 261, thesprings 265 and 267 on the arms 220 and 221 are compressed. Each pair ofarms 210-210 and 211-221 continue to move inward toward each other untilthe springs are compressed by a predetermined holding force, for examplea force of 5 to 20 Newtons. Once the holding force is reached, the armsare stopped and retain the registration carrier securely clamped betweenthe stop surfaces 263 on each pair of arms during the bending process.At no time is the glass contacted by anything other than the stage 107,the registration rollers 109A and 109B and the clamp 113. The stopsurfaces on the arms only contact the caps 261 that protect the cornersof the ceramic stage 107. The surface of the glass sheet thereforeretains its pristine surface. It will be appreciated that the referencesurfaces may be alternatively located on the side rails 225, 226 of thecarrier frame 108, rather than on the protective caps on the stage.

The heaters 222 are then activated to heat the portions of the glasssheet to be bent to the bending temperature. Once the portions of theglass sheet to be bent are heated to the bending temperature, then theforce applying devices 224 are activated to apply a downward force onthe edge portions 3 a and 5 a of the glass sheet to facilitate bendingof the glass sheet in the area of the edges 103 and 105 of the stage107. After bending, the heaters and the force applying devices aredeactivated and the arms 210, 211 and 220, 221 are retracted away fromthe registration carrier 100. As the lift arms 251 are retracted, thelift rollers 253 move out from under the registration carrier and theregistration carrier drops back down into engagement with the conveyorframe, with the bearings 231 and 237 engaged in the forks 241 and 243.The clamp 113 may be opened prior to cooling the formed glass sheet fromthe bending temperature, in order to remove the contact surfaces 111from the glass sheet and avoid marring of the glass sheet during coolingand contraction of the glass sheet. The conveyor then moves theregistration carrier and the formed/bent glass sheet 1 out of thebending zone and into the cooling zone 27 and out of the bending oven.The shaped and cooled glass sheets are then unloaded from the stage. Newflat glass sheets are then loaded onto the vacated stage and the processis repeated.

With the previously described structure, the inner ends of the arms210-220 and 211-221, and therefore the heaters 222 and the optionalforce applying device 224 carried on the inner ends of the arms, areprecisely located and aligned relative to the edges 103 and 105 of thestage 107 simply by contacting and pressing the stop surfaces 255 oneach of the arms against the reference surfaces 263 on each of the caps261 on the stage 107. By lifting the registration carrier off theconveyor, such that the registration carrier “floats” or rolls/slides onthe top of the lift rollers 253, the registration carrier is free totranslate and rotate on the lift rollers, such that the registrationcarrier and the stage “self align” with the ends of the arms when thestop surfaces 255 press against the reference surfaces 263. Since theglass sheet is precisely mounted on the stage, the heaters and forceapplying devices are also precisely located relative to and aligned withthe glass sheet.

This contact between the stop surfaces 255 on the arms and the referencesurfaces 263 on the caps is maintained by the spring loaded pressure(for example 5 to 20 Newtons) applied by the arms against the caps. Thisstructure allows for simple and automatic vertical, lateral and angularpositioning of the stage 107 and glass 1 relative to the heating andforce applying devices on the arms. There is no need for expensive, hardto program controllers, stepper motors or position sensors in order toprecisely align the heaters and the force applying devices with theglass sheet on the registration carrier.

Locating the stop surfaces 255 on the arms closely adjacent to theheaters and the force applying devices on the arms minimizes the effectof thermal expansion of the arms on the position of the heaters and theforce applying devices. As schematically illustrated in FIG. 12, thethermal expansion of just the mechanical elements between the stopsurfaces on the arms and the operative portions of the heater and theforce applying devices, e.g. the portions indicated by arrow H₁ in FIG.12, effects the position of the heaters and force applying devicesrelative to the stage and the glass sheet 1. Should any other portionsof the arm 210, the conveyor, the bending oven 21 or floor thermallyexpand, it will have no effect on the position of the heaters and forceapplying devices relative to the stage 107. In an arrangement where theposition of the heaters and force applying devices relative to the stageand the glass sheet is controlled by moving mechanisms 215, 217 locatedoutside the bending oven 21, then the thermal expansion the bending oven21, the floor, the moving mechanisms 215, 217, and virtually the entirelength of the arms 210, 220, as indicted by arrows H₂ in FIG. 13, willhaven an effect on the position of the heaters 112, 222 and the forceapplying devices 114, 224. As such the heaters and the force applyingdevices should be mounted to the arms as close as possible to the stopsurfaces on the arms in order to minimize the effects of thermalexpansion on their positioning relative to the glass sheet on the stage.

The system and structures described herein provide for reliable andprecise bending of relatively large sheets of relatively high CTE ofglass, as well as of relatively thin, relatively large sheets ofrelatively high CTE of glass. With this construction the heaters and theforce applying devices may be precisely located relative to the stageand the glass sheet with an accuracy within tenths of a millimeter, e.g.+/−0.03 mm.

According the further embodiments hereof, the systems and processesdescribed and claimed herein may be employed to bend more than one glasssheet on a carrier at a time. For example, the stage may be equippedwith 2 to 4 pairs of registration elements 109A and 109B and 2 to 4clamps 113, in order to precisely locate and secure 2 to 4 sheets ofglass on the stage for precise bending of 1 or 2 edges of each of the 2to 4 glass sheets in the bending oven at substantially the same time.Additional pairs of arms and bending mechanisms as described herein maybe provided in the oven as needed for bending 2-4 glass sheets.

What is claimed is:
 1. An apparatus for precisely bending a glass sheet,comprising: an oven for heating the glass sheet to a processingtemperature between the annealing temperature and the softeningtemperature of the glass sheet; a stage having a top support surface forsupporting a sheet of glass, a first edge, an opposing second edge, anda pair of outward facing first reference surfaces on the first edge ofthe stage adjacent to ends of the first edge of the stage; a pair offirst arms having inner ends extending into the oven from a first sideof the oven, a first bending mechanism mounted on the inner ends of thefirst pair of arms inside the oven for bending a first edge portion of aglass sheet on the stage down over the first edge of the stage, and aninward facing first stop surface provided near the inner end of each ofthe first arms in opposition to the pair of first reference surfaces; apair of second arms having inner ends extending into the oven from asecond side of the oven, and an inward facing second stop surfaceprovided near the inner end of each of the second arms in opposition tothe second edge of the stage; a first moving mechanism for moving thepair of first arms inward toward and outward away from the first edge ofthe stage; and whereby when the stage is located in the oven with aglass sheet to be bent supported on the support surface of stage with afirst edge portion of the glass sheet to be bent extending beyond thefirst edge of the stage, the first arms are moved inward toward thestage and the second arms are moved inward toward the stage until thefirst stop surfaces contact the first reference surfaces and the secondstop surfaces contact the second edge of the stage, whereby the stage isheld between the first stop surfaces and the second stop surfaces withthe first edge of stage and the first edge of the glass sheet isprecisely located relative to and aligned with the first bendingmechanism.
 2. An apparatus as in claim 1, wherein at least one of thepair of first arms and the pair of second arms are spring loaded and thefirst arms and the second arms are moved inward until the spring loadarms are compressed and apply pressure on the edge of the stage.
 3. Anapparatus as in claim 1, further comprising a lift arm on the inner endsof each of the first arms and the second arms that extend inward fromthe first and second stop surfaces; wherein when the first arms aremoved inward toward the stage and the second arms are moved inwardtoward the stage, the lift arms engage an under-side of the stage andlift the stage such that the stage is resting on the lift arms and thestage is free to translate and rotate on the lift arms, whereby as thefirst stop surfaces contact the first reference surfaces and the secondstop surfaces contact the second edge of the stage, whereby the stagetranslates and rotates on the lift arms until all of the first stopsurfaces are contacting the first reference surfaces and all of thesecond stop surfaces are contacting the second edge of the stage,whereby the first edge of the stage and the first edge of the glasssheet are precisely located relative to and aligned with the firstbending mechanism.
 4. An apparatus as in claim 3, wherein at least oneof the pair of first arms and the pair of second arms are spring loadedand the first arms and second arms are moved inward until the springload arms are compressed and apply pressure on the edge of the stage. 5.An apparatus as in claim 1, further comprising: a pair of outward facingsecond reference surfaces on the second edge of the stage adjacent toends of the second edge of the stage; and a second bending mechanismmounted on the inner ends of the second pair of arms inside the oven;whereby when the stage is located in the oven with a glass sheet to bebent supported on the support surface of stage with a first edge portionof the glass sheet to be bent extending beyond a first edge of the stageand a second edge portion of the glass sheet to be bent extending beyondthe second edge of the stage, the first arms are moved inward toward thestage and the second arms are moved inward toward the stage until thefirst stop surfaces contact the first reference surfaces and the secondstop surfaces contact the second reference surfaces, whereby the stageis held between the first stop surfaces and the second stop surfaceswith the first edge of stage and the first edge of the glass sheetprecisely located relative to and aligned with the first bendingmechanism and the second edge of stage and the second edge of the glasssheet precisely located relative to and aligned with the second bendingmechanism.
 6. An apparatus as in claim 5, wherein at least one of thepair of first arms and the pair of second arms are spring loaded and thefirst arms and second arms are moved inward until the spring load armsare compressed and apply pressure on the edge of the stage.
 7. Anapparatus as in claim 1, wherein the stage further comprises: a thirdedge extending between the first edge of the stage and the second edgeof the stage; and a first registration element extending upward form thesupport surface of the stage adjacent to the third edge of the stage;and a second registration element extending upward from the supportsurface of the stage adjacent to the third edge of the stage; the firstregistration element and the second registration element being locatedon the stage to define a reference line oriented at a desiredorientation with respect to the first edge of the stage, whereby when aglass sheet having a first edge portion to be bent is located on thesupport surface with a reference edge of the glass sheet extending fromthe first edge in contact with both the first registration element andthe second registration element, the first edge portion of the glasssheet is aligned with the first edge of the stage.
 8. An apparatus as inclaim 7, wherein the stage further comprises a clamp mounted adjacent tothe third edge of the stage, the clamp having a clamp surface forclamping a glass sheet in place on the support surface; whereby when theglass sheet is located on the support surface with the reference edge ofthe glass sheet in contact with both the first registration element andthe second registration element and a reference point on the glass sheetis aligned with and clamped in place on the stage by the clamp surface,the glass sheet is precisely located and secured in place on the stagewith the first edge portion of the glass sheet aligned with andextending a first desired distance beyond the first edge of the stage.9. An apparatus as in claim 8, wherein the clamp surface is formed oftwo or more separate contact surfaces.
 10. An apparatus as in claim 8,further comprising: a pair of outward facing second reference surfaceson the second edge of the stage adjacent to each end of the second edgeof the stage; and a second bending mechanism mounted on the inner endsof the second pair of arms inside the oven; whereby when the glass sheetis located on the support surface with the reference edge of the glasssheet in contact with both the first registration element and the secondregistration element and a reference point on the glass sheet is alignedwith and clamped in place on the stage by the clamp surface, the glasssheet is precisely located and secured in place on the stage with thefirst edge portion of the glass sheet aligned with and extending a firstdesired distance beyond the first edge of the stage and the second edgeportion of the glass sheet aligned with and extending a second desireddistance beyond the second edge of the stage; and whereby when the firstarms are moved inward toward the stage and the second arms are movedinward toward the stage until the first stop surfaces contact the firstreference surfaces and the second stop surfaces contact the secondreference surfaces, the stage is held between the first stop surfacesand the second stop surfaces with the first edge of stage and the firstedge of the glass sheet is precisely located relative to and alignedwith the first bending mechanism and second edge of stage and the secondedge of the glass sheet is precisely located relative to and alignedwith the second bending mechanism.
 11. An apparatus as in claim 10,wherein the first bending mechanism and second bending mechanism eachinclude a biasing apparatus for pushing and bend the corresponding firstedge portion of the glass sheet and the second first edge portion of theglass sheet down over a corresponding one of the first edge of the stageand a second edge of the stage.
 12. An apparatus as in claim 11, whereinthe first bending mechanism and second bending mechanism each include alocal heating apparatus for heating the corresponding first edge portionof the glass sheet and the second edge portion of the glass sheet to theprocessing temperature.
 13. An apparatus as in claim 10, wherein thefirst bending mechanism and second bending mechanism each include alocal heating apparatus for heating the corresponding first edge portionof the glass sheet and the second edge portion of the glass sheet to theprocessing temperature.
 14. An apparatus as in claim 10, furthercomprising a lift arm on the inner ends of each of the first arms andthe second arms that extend inward from the first and second stopsurfaces; wherein when the first arms are moved inward toward the stageand the second arms are moved inward toward the stage, the lift armsengage an under-side of the stage and lift the stage such that the stageis resting on the lift arms and the stage is free to translate androtate on the lift arms, whereby as the first stop surfaces contact thefirst reference surfaces and the second stop surfaces contact the secondreference surfaces the stage translates and rotates on the lift armsuntil all of the first stop surfaces are contacting the first referencesurfaces and all of the second stop surfaces are contacting the secondreference surfaces, whereby the first edge of the stage and the firstedge of the glass sheet are precisely located relative to and alignedwith the first bending mechanism and the second edge of the stage andthe second edge of the glass sheet are precisely located relative to andaligned with the second bending mechanism.
 15. An apparatus as in claim1, wherein stage comprises a low coefficient of thermal expansion (CTE)material that is substantially inelastic in a processing temperaturerange of from about 20° C. to about 750° C. range.
 16. An apparatus asin claim 15, wherein the stage is formed of a material form the groupcomprising ceramic, glass-ceramic, and silicon carbide (SiC) material.17. An apparatus as in claim 15, wherein the stage is no more the 1 cmin order to further minimize the thermal inertia of the stage andminimize the thermal impact of the stage on the glass sheet duringprocessing.